1. Field of the Invention
The present invention relates to a method of growing a ferroelectric film employed in a semiconductor device, and particularly to a ferroelectric thin film memory which provides less leakage current and a high yield.
2. Description of the Related Art
With the advances in deposition or growth technology in recent years, a non-volatile memory or a ferroelectric capacitor has extensively been developed as a semiconductor element using a ferroelectric film. An example of such a non-volatile memory includes a ferroelectric random access memory (abbreviated as "FeRAM") using a polarization inverted characteristic of a ferroelectric thin film. Use of a ferroelectric film as a high-dielectric-constant film is known as a capacitor. Examples of ferroelectric film include a bismuth layered crystal structure oxide such as Sr.sub.2 Bi.sub.2 Ta.sub.2 O.sub.9 (SBT), SrBi.sub.2 (Ta, Nb) O.sub.4 (SBTN), or a perovskite structure oxide such as PbZrO (PZT). A process for growing this type of ferroelectric film is generally shown in FIGS. 1A through 1D.
A lower electrode 2 is formed over a silicon substrate 1 used as a bed by means of platinum (Pt) or iridium oxide (IrO.sub.2) or the like (see FIG. 1A). A precursor solution 3 in which SBT is used as a ferroelectric material or substance is dissolved, is applied to the lower electrode 2 to thereby form a uniformly applied film by a spin coat method (see FIG. 1B).
Thereafter, the precursor solution is dried and subjected to calcination anneal at 800.degree. C. or a temperature greater than a crystallization temperature for 30 minutes in an oxygen atmosphere to thereby obtain a crystallized SBT film 4 (see FIG. 1C). The process steps of FIGS. 1B and 1C for applying and calcining the precursor solution may be repeated plural times to reach a desired thickness, thereby forming a ferroelectric SBT film 5 having a desired thickness.
However, a problem arises in that since the ferroelectric material is strong in crystal anisotropy when the conventional growth process referred to above is used, irregularities or projections and depressions 6 are formed over the surface of the ferroelectric film 5 or voids 7 are generated in the ferroelectric film 5 as shown in FIG. 1D.
Applying the precursor solution plural times and then drying it to form the SBT film may principally lead to irregularities, and formation of voids. Therefore, leakage current may be increased between electrodes of a semiconductor memory using a ferroelectric film or a short may occur between the electrodes, thus reducing the reliability of the ferroelectric memory.